Conventional vehicle braking systems employ a brake pedal assembly having a brake pedal coupled to a master cylinder. The brake pedal is actuated by the vehicle operator to control the amount of braking torque applied to the wheels of the vehicle via friction braking with the use of hydraulic pressure or electromechanical force. In a brake-by-wire braking system, where the operator's braking request is generally independent of the brake torque, certain characteristics of the brake pedal are sensed and processed in accordance with a predetermined operating curve. For example, brake systems commonly employ either a stroke position sensor to sense the travel displacement of the brake pedal or a pressure sensor to sense the amount of pressure in the brake master cylinder, while some brake systems employ both sensors. An electronic brake controller processes the sensed information, computes the braking torque requested, and generates a control signal to control the amount of torque applied to the brakes of the vehicle. In conventional brake systems, the brake feel characteristics, which may include pedal force versus pedal travel, deceleration versus work, stiffness versus work, deceleration versus pedal force, and deceleration versus pedal travel, are typically permanently defined.
The aforementioned conventional brake system characteristics are generally fixed and therefore cannot be adjusted to accommodate various needs of different drivers. Instead, the position of other accessories in the vehicle, such as the driver's seat, the steering wheel, and the brake and accelerator pedal assembly, may be adjusted to allow the driver to select a preferred position that accommodates the driver's stature and comfort. Despite adjustments of the aforementioned vehicle accessories, the brake pedal must still be actuated with the same amount of effort and pedal travel to achieve the same braking effect. The brake system therefore does not fulfill all the needs for certain vehicle operators. For example, operators who are generally shorter in height may prefer a shortened brake pedal travel to compensate for their lower pedal force and pedal travel to achieve a certain braking torque or deceleration, while taller operators typically prefer an extended brake pedal travel and force to achieve the same braking torque or deceleration.
One approach for adjusting the braking effort in a vehicle is set forth in U.S. Pat. No. 5,378,052, which discloses an electronic brake pedal adjustment apparatus for setting certain braking characteristics by providing the driver with a manual input in the form of a slide control input device, so that the driver of the vehicle can manually adjust the desired braking characteristics. The apparatus of the aforementioned issued patent requires a separate manual input device that requires the driver of the vehicle to first determine the need for a change in braking effort, and then to physically adjust the input device to achieve the desired braking characteristic. Accordingly, the driver may have to manually readjust the manual input, particularly when different drivers having different anatomical dimensions use the same vehicle. In addition, the driver generally may not be accustomed to adjusting the input to the most advantageous position.
Accordingly, there is a need for a variable brake system in a vehicle that adjusts the braking effort to accommodate the needs of the driver.